Electrical equipment such as transformers use fluids such as castor oil, mineral oil and synthetic oils for insulation purposes. The parameters of the fluid are indicative of incipient faults in the electrical equipment. The parameters of the fluid among other things include information about the concentration of dissolved gases. Examples of dissolved gases include carbon monoxide, carbon dioxide, hydrocarbons, oxygen and nitrogen. Specifically, carbon monoxide and carbon dioxide increase in concentration with thermal aging and degradation of insulation of the electrical equipment. Furthermore, hydrocarbons such as acetylene and ethylene increase in concentration due to dielectric breakdown caused by corona and arcing. Further, concentrations of oxygen and nitrogen are indicative of condition of a gas pressurizing system of the equipment. Accordingly, the dissolved gases may be extracted from equipment (such as transformers) and analyzed to determine incipient faults in the equipment.
Typically, absorption spectroscopy technique may be used for analyzing a gas-mixture. For increased sensitivity, wavelength modulation absorption spectroscopy technique may be used to analyze a gas-mixture. The wavelength modulation absorption spectroscopy technique, for example, employs irradiation of a gas-mixture by a scanned modulated-light-beam (hereinafter “incident modulated-light-beam”) resulting in absorption of a portion of the incident modulated-light-beam by gases present in the gas-mixture, and transmission of rest (hereinafter referred to as “transmitted-light-beam”) of the incident modulated-light-beam from the gas-mixture. Due to absorption of the portion of the incident modulated-light-beam, the intensity of the transmitted-light-beam is less than the incident modulated-light-beam at an absorption peak of an individual gas present in the gas-mixture. A detector detects the transmitted-light-beam to generate a signal representative of intensity of the transmitted-light-beam as a function of wavelength. For example, the Beer Lambert law may be used to measure concentrations of the gases present in the gas-mixture based on an amount of absorption of the incident modulated-light-beam by the gases. The amount of absorption of the incident modulated-light-beam, for example, may be determined based on the intensity of the incident modulated-light-beam and the signal representative of the intensity of the transmitted-light-beam. The gas concentration, for example, may also be determined using the amplitude of the intensity signal at the second harmonic of the modulation frequency.
Typically, the incident modulated-light-beam characterized by a modulation frequency of if and a modulation amplitude of 2.2 times half-width half-maximum (HWHM) of the absorption peak is used in wavelength modulation absorption spectroscopy techniques. Typically the modulation amplitude of 2.2 times half-width half-maximum (HWHM) of the absorption peak is believed to result in generation of an optimal 2 f signal. The modulation frequency generally used is much larger than the scan frequency with no other special criterion. However, usage of the 2.2 times HWHM modulation amplitude and any modulation frequency may result in high noise (for example etalon noise and electronic noise) in the signal representative of the intensity of the transmitted-light-beam resulting in low signal-to-noise ratio. The low signal-to-noise ratio may lead to inaccurate analysis of the gas-mixture. For example, the low signal to noise ratio may result in inaccurate determination of the concentrations of the gases present in the gas-mixture.
Accordingly, it is desirable to provide systems and methods that may provide accurate measurements of gases present in a gas-mixture. Particularly, it is desirable to provide systems and methods that may determine optimal modulation frequency and optimal modulation amplitude for different wavelengths of an incident modulated-light-beam to increase the signal-to-noise ratio resulting in accurate measurements of gases present in a gas-mixture.